SF bug #1473760 TempFile can hang on Windows.

Python 2.4 changed ntpath.abspath to do an import
inside the function.  As a result, due to Python's
import lock, anything calling abspath on Windows
(directly, or indirectly like tempfile.TemporaryFile)
hung when it was called from a thread spawned as a
side effect of importing a module.

This is a depressingly frequent problem, and
deserves a more general fix.  I'm settling for
a micro-fix here because this specific one accounts
for a report of Zope Corp's ZEO hanging on Windows,
and it was an odd way to change abspath to begin
with (ntpath needs a different implementation
depending on whether we're actually running on
Windows, and the _obvious_ way to arrange for that
is not to bury a possibly-failing import _inside_
the function).

Note that if/when other micro-fixes of this kind
get made, the new Lib/test/threaded_import_hangers.py
is a convenient place to add tests for them.

3 files changed, 84 insertions, 22 deletions

diff --git a/Lib/ntpath.py b/Lib/ntpath.py
index 5dd5f1a..7a79b53 100644
--- a/Lib/ntpath.py
+++ b/Lib/ntpath.py
@@ -481,27 +481,28 @@ def normpath(path):
 
 
 # Return an absolute path.
-def abspath(path):
-    """Return the absolute version of a path"""
-    try:
-        from nt import _getfullpathname
-    except ImportError: # Not running on Windows - mock up something sensible.
-        global abspath
-        def _abspath(path):
-            if not isabs(path):
-                path = join(os.getcwd(), path)
-            return normpath(path)
-        abspath = _abspath
-        return _abspath(path)
-
-    if path: # Empty path must return current working directory.
-        try:
-            path = _getfullpathname(path)
-        except WindowsError:
-            pass # Bad path - return unchanged.
-    else:
-        path = os.getcwd()
-    return normpath(path)
+try:
+    from nt import _getfullpathname
+
+except ImportError: # not running on Windows - mock up something sensible
+    def abspath(path):
+        """Return the absolute version of a path."""
+        if not isabs(path):
+            path = join(os.getcwd(), path)
+        return normpath(path)
+
+else:  # use native Windows method on Windows
+    def abspath(path):
+        """Return the absolute version of a path."""
+
+        if path: # Empty path must return current working directory.
+            try:
+                path = _getfullpathname(path)
+            except WindowsError:
+                pass # Bad path - return unchanged.
+        else:
+            path = os.getcwd()
+        return normpath(path)
 
 # realpath is a no-op on systems without islink support
 realpath = abspath
diff --git a/Lib/test/test_threaded_import.py b/Lib/test/test_threaded_import.py
index dc27d4e..0642d25 100644
--- a/Lib/test/test_threaded_import.py
+++ b/Lib/test/test_threaded_import.py
@@ -6,7 +6,7 @@
 # randrange, and then Python hangs.
 
 import thread
-from test.test_support import verbose, TestSkipped
+from test.test_support import verbose, TestSkipped, TestFailed
 
 critical_section = thread.allocate_lock()
 done = thread.allocate_lock()
@@ -25,6 +25,23 @@ def task():
     if finished:
         done.release()
 
+def test_import_hangers():
+    import sys
+    if verbose:
+        print "testing import hangers ...",
+
+    from test import threaded_import_hangers
+
+    try:
+        if threaded_import_hangers.errors:
+            raise TestFailed(threaded_import_hangers.errors)
+        elif verbose:
+            print "OK."
+    finally:
+        # In case this test is run again, make sure the helper module
+        # gets loaded from scratch again.
+        del sys.modules['test.threaded_import_hangers']
+
 # Tricky:  When regrtest imports this module, the thread running regrtest
 # grabs the import lock and won't let go of it until this module returns.
 # All other threads attempting an import hang for the duration.  Since
@@ -53,5 +70,7 @@ def test_main():        # magic name!  see above
             print "OK."
     done.release()
 
+    test_import_hangers()
+
 if __name__ == "__main__":
     test_main()
diff --git a/Lib/test/threaded_import_hangers.py b/Lib/test/threaded_import_hangers.py
new file mode 100644
index 0000000..b21c52f
--- /dev/null
+++ b/Lib/test/threaded_import_hangers.py
@@ -0,0 +1,42 @@
+# This is a helper module for test_threaded_import.  The test imports this
+# module, and this module tries to run various Python library functions in
+# their own thread, as a side effect of being imported.  If the spawned
+# thread doesn't complete in TIMEOUT seconds, an "appeared to hang" message
+# is appended to the module-global `errors` list.  That list remains empty
+# if (and only if) all functions tested complete.
+
+TIMEOUT = 10
+
+import threading
+
+import tempfile
+import os.path
+
+errors = []
+
+# This class merely runs a function in its own thread T.  The thread importing
+# this module holds the import lock, so if the function called by T tries
+# to do its own imports it will block waiting for this module's import
+# to complete.
+class Worker(threading.Thread):
+    def __init__(self, function, args):
+        threading.Thread.__init__(self)
+        self.function = function
+        self.args = args
+
+    def run(self):
+        self.function(*self.args)
+
+for name, func, args in [
+        # Bug 147376:  TemporaryFile hung on Windows, starting in Python 2.4.
+        ("tempfile.TemporaryFile", tempfile.TemporaryFile, ()),
+
+        # The real cause for bug 147376:  ntpath.abspath() caused the hang.
+        ("os.path.abspath", os.path.abspath, ('.',)),
+        ]:
+
+    t = Worker(func, args)
+    t.start()
+    t.join(TIMEOUT)
+    if t.isAlive():
+        errors.append("%s appeared to hang" % name)